Field
The present disclosure generally relates to a summing amplifier.
Description of Related Art
Persons of ordinary skill in the art understand terms and basic concepts related to microelectronics that are used in this disclosure, such as “voltage,” “current,” “bias,” “signal,” “clock,” “node,” “logical signal,” “trip point,” “inverter,” “power,” “ground,” “switch,” “MOS (metal oxide semiconductor,” “PMOS (p-channel metal oxide semiconductor),” “NMOS (n-channel metal oxide semiconductor),” “transistor,” “source,” “gate,” “drain,” “resistor,” “capacitor,” “transconductance,” and “common mode.” Terms and basic concepts like these are apparent to those of ordinary skill in the art and thus will not be explained in detail here.
A summing amplifier receives a plurality of input signals and outputs an output signal that is a weighted sum of said plurality of input signals. A particular application of interest is a decision feedback equalizer (DFE), wherein a summing amplifier is used to equalize a signal. DFE is known to those of ordinary skill in the art of high-speed SerDes (Serializer/Deserializer) receiver and thus not described in detail here. Park et al presented a summing amplifier in “A 7 Gb/s 9.3 mW 2-Tap Current-Integrating DFE Receiver,” IEEE ISSCC Dig. Tech. Papers, 2007, pp. 230-599. A shortcoming of the summing amplifier is that, the common-mode voltage of the output is difficult to control accurately. Although Park et al employed a calibration circuit to control the common-mode voltage of the output of the summing amplifier, the calibration circuit is a duplicate circuit. In other words, the calibration is performed on the duplicate circuit, instead of directly on the summing amplifier. Therefore, the accuracy of the common-mode voltage of the output of the summing amplifier is questionable and subject to a mismatch between the duplicate circuit and the summing amplifier. Another shortcoming of the summing amplifier is: the summing amplifier needs to be reset periodically, and a power supply circuit that supplies power to the summing amplifier will be disturbed whenever the summing amplifier is reset.
An exemplary embodiment of a summing amplifier has an accurate output common-mode voltage control and exhibits less disturbance to the power supply circuit.